BOGOTA, Colombia -- A bus carrying tourists in southwestern Colombia plunged off a ravine on Sunday evening, killing 23 passengers, including six children, and injuring another 14 people, officials said. The accident occurred between 279 miles (450 kms) southeast of Bogota near the resort town of Lago Calima, as the tourists were returning from a weekend trip. The city's mayor and local police cited an unspecified mechanical failure in the trans-Tulua tour bus as the cause of the accident.